In mining and construction, most excavating equipment ordinarily include a series of spaced apart teeth mounted across a bucket lip. The teeth project forwardly to engage and break up the material to be gathered in the bucket. As can be appreciated, the teeth are subjected to highly abrasive conditions and thus experience considerable wearing.
In order to minimize the loss of material due to replacement of parts, the teeth are manufactured as two parts--an adapter and a point. The adapter is attached (e.g., by welding) to the bucket's lip and includes a forwardly projecting nose. The point defines a rearwardly opening socket into which the adapter nose is received and includes a front digging edge. The point substantially envelops the adapter nose and thereby tends to protect the nose from wear. As a result, however, the point is subjected to abrasive conditions and must be frequently replaced. In general, five to thirty points may be successively mounted onto a single adapter, depending upon the severity of the application. Due to the large loads and impacts applied to the teeth, it is essential that the points be securely locked to the adapters. Yet, since the points are changed in the field, the locks must be easily set and released. While many styles of locks have been developed, they commonly include the use of a lock pin.
According to one common arrangement, the point and adapter nose are each provided with a central locking aperture. When the parts are assembled, the apertures are aligned to enable receipt of a lock pin. In some cases, a rigid pin is used in combination with a resilient keeper member. The keeper member is employed to hold the pin in the apertures and to tighten the engagement of the point over the adapter nose. An example of this type of tooth is disclosed in U.S. Pat. No. 2,312,802 to Crawford. In an alternative arrangement, a sandwich pin may be used without a separate keeper member. In general, a sandwich pin is comprised of a rigid portion to provide adequate strength to hold the point to the adapter and a resilient portion to secure the pin in place and tighten the connection of the parts. An example of this construction is set forth in U.S. Pat. No. 4,823,487 to Robinson.
Teeth with these constructions, however, experience a number of shortcomings. The formation of central apertures in both the point and adapter nose weakens the overall strength of the tooth. In addition, under heavy longitudinal loading of the point, the keeper or elastomeric portion of the lock is forced to accept loads beyond its capacity. This phenomenon is exacerbated in situations involving a partially worn adapter nose. Frequent or cyclic overloading of the resilient component can result in premature failure of the member. Failure of the keeper or elastomer can lead to loss of the pin and hence the point. If a point is lost, the adapter will be quickly ruined as the nose is not made to resist highly abrasive conditions.
In use, points are often subjected to jacking or fluttering forces. More specifically, as the point is forced through the ground it is constantly exposed to endless variations in resistance caused by rocks, roots, concrete and other discontinuities in the ground. These variations are magnified in front end loaders which are driven forward along the ground and thus experience additional vertical and transverse movements of the bucket during loading. In any event, these variations in resistance tend to apply forces having significant vertical components to the points. Moreover, the loads generally reverse directions at a rapid rate on the point such that upward and downward forces act repeatedly on the points. In large operations loads upwards of 200,000 pounds would not be unexpected.
As can be appreciated, a vertical load on the front edge of the point tends to apply a large moment force to the point, which if not resisted, would rotate the point off the adapter nose. These moment forces also apply large stresses on the bearing faces of the nose and cause deformation and wear to the nose. Moreover, as can be seen in FIG. 2 of the '487 patent, the rear wall of the aperture in the point engages the rear of the lock pin. As the point is forced to rotate under the moment force, a corresponding force (i.e., one with a vertical component) is applied to the pin. With constant reversing of the loads in jacking forces, the pin can be worked free and ejected from the aperture even without failure of the elastomer or over-wearing of the components. Although the unique construction of the adapter nose and the socket of the point in U.S. Pat. No. 4,231,173 to Davis has to some degree alleviated the problem, it does not provide a perfect solution for all applications.
Ejection of the pin can be partially alleviated if the lock pin is inserted through a set of aligned apertures oriented in a horizontal direction (i.e., parallel with the lip of the bucket). A tooth with this construction is referred to as a side locking tooth. An example of such a construction is shown in U.S. Pat. No. 2,669,153 to Launder. With this construction, rotational movements of the point in a vertical plane do not apply forces along the pin's axis to eject the pin. Nevertheless, significant transverse jacking forces can be applied to the point and thus transmitted to the pin along its axis. Moreover, because of the typical close spacing of the teeth on a bucket, very little access space is provided to insert and remove the pins. In the field, the pins are usually manually inserted and removed by an individual using a pointed tool and a sledge hammer. Accordingly, difficulties in replacing the points are frequently encountered. Due to these shortcomings, teeth with this construction have become known as "Knuckle Busters."
In all of these lock assemblies, the point is movable farther up on the adapter nose as the nose becomes worn. As a result, the elastomeric element must expand a corresponding amount to maintain a tight fit and prevent loss of the pin. Once the maximum expansion of the member is reached, the pin may be lost or ejected. Therefore, in order to maximize the life of the components the apertures defined through the point and adapter nose, irrespective of whether they are vertical or horizontal apertures, are typically constructed so that the pin is initially inserted into a very tight arrangement. A tight fit leads to difficulty in inserting and removing the pin. Difficulty in replacing the points causes increased downtime and a greater likelihood that workers may avoid timely replacement of the points.
To overcome many of the disadvantages associated with central and side locking teeth, excavating teeth with external locking constructions have been developed. An example of a popular external locking tooth is shown in U.S. Pat. No. 4,965,945 to Emrich. As can be seen in FIG. 3 of the '945 patent, the point is provided with a pair of vertically spaced lugs which are placed to each side of a central ledge or shoulder formed on the side of the adapter nose. A rigid lock pin is inserted vertically between the lugs of the point and the ledge of the adapter nose to couple the components together. The pin preferably has an arcuate configuration which is slightly flexed (i.e., straightened) when inserted to tighten the overall assembly of the tooth. A transverse resilient plug is provided to lock the pin in place. The plug is comprised of a helical spring encased in a resilient foam material.
This external locking construction avoids the formation of enlarged apertures in the components and thereby provides a stronger tooth. Further, the transverse orientation of the resilient plug shields it from the major forces applied to the point. Overloading of the plug is thus avoided. However, this lock pin and plug combination does not attain the advantages of a one-piece lock.
An alternate external locking construction using a sandwich lock pin, as shown in U.S. Pat. No. 5,152,088 to Hahn, has also been used. In this construction, the adapter nose has a vertical channel defined along one of its sides to receive the pin. The point includes a rearwardly extending tongue in opposed relation to the channel and an inwardly directed lug. The lock pin is comprised of rigid front and rear faces which resist the major loads applied to the point, and an elastomer provided with a pair of transverse locking detents adapted for receipt in recesses defined in the adapter nose and the tongue. While this construction performs well in smaller sized teeth, it does not provide an adequate solution for all circumstances.
The present invention pertains to a tooth, comprised of a point, an adapter and a sandwich pin, which has a construction unknown in the prior art. The tooth of the present invention is much less susceptible to pin loss due to overloading of a pin elastomer, the effects of jacking forces or wear to the adapter nose. Moreover, the points can be readily replaced in the field.
According to one aspect of the invention, an excavating tooth is comprised of an adapter, a point, and a sandwich pin. The adapter includes a forwardly projecting nose and an opening associated with the nose. The point includes a front digging edge, a socket which is matingly received over the adapter nose, and a first opening which aligns with the adapter opening for receipt of the sandwich pin. The point further includes a second opening proximate to the first opening. The pin is comprised of a rigid casing and a plurality of independently depressible protrusions. One of the protrusions resiliently engages a portion of the adapter nose to tighten the attachment of the point onto the nose. At least one other protrusion extends into the second opening of the point to securely lock the pin to the point. The independent operation of the protrusions functions to alleviate pin loss due to overloading of the elastomeric material, the effects of jacking forces or wear to the adapter nose.
According to another aspect of the invention, the sandwich pin includes a rigid casing member and a plurality of elastomeric members. One of the elastomeric members forms a first protrusion which engages and presses against a portion of the adapter nose to effect tightening of the point onto the nose. At least one other elastomeric member forms a second protrusion which functions to lock the pin to the point. The locking elastomer is separate and apart from the tightening elastomer and is shielded from the major forces applied to the point by the rigid casing. Since the locking elastomer is isolated from the loading forces it cannot be overloaded. As a result, pin loss due to failure of an elastomeric member is virtually eliminated. The use of a separate locking elastomer further reduces the likelihood of pin ejection under jacking forces.
In another aspect of the invention, the rigid casing of the pin is matingly received and held in at least a portion of the pin opening defined by the point. In this way, the point independently holds the pin, regardless of the longitudinal position of the point on the adapter nose. This independent holding of the pin causes the pin to move with the point as it is repeatedly jerked under jacking forces. This integral movement of the pin with the point virtually eliminates the thrust forces formerly applied by the point in ejecting the pin from the opening. Hence, the pin is substantially prevented from being lost due to jacking forces or wear to the adapter nose. The holding of the pin by the point also permits the assembly of a "looser" tooth construction. In other words, since the pin is held by the point, the pin does not need to be inserted into a tight tooth assembly. As a result, the pin opening in the present invention can be formed with a minimum clearance to permit easy driving of the pin in the field.
In the tooth illustrated in FIGS. 5-8 of the '487 patent, the lock pin is received into a slot defined in the point. As seen in FIG. 8 thereof, the slot includes shoulders which are shown to matingly receive the pin. However, a closer inspection reveals that the construction is wholly unworkable. More specifically, when the pin is inserted, it is driven vertically downward into the aligned openings. As seen in FIG. 5 thereof, the pin has a central segment rearward of the shoulders which is broader than its end portions. The mating receipt of the pin's end portions in the point openings (as seen in FIG. 8) would preclude the passage of the broader central segment through the same opening. As a result, this patent fails to provide a useful teaching in this regard.
According to another aspect of the invention, a point of an external locking tooth includes a pair of vertically spaced apart lugs disposed rearwardly of the point's body. The lugs are attached to the body by an ear which forms an extension of one of the point's sidewalls. The ear attaches to a sidewall of the point with broad arcuate transition segments at the top and bottom ends of the ear. This broad arcuate configuration is important in maintaining stress levels at this juncture point within a range of acceptable levels. In addition, the body, the ear and the lugs collectively define an opening in which the lock pin is received. A boss is provided opposite each lug to facilitate mating receipt of the pin in the point opening. However, the provision of such a boss requires the formation of a sharper corner between the ear and the body than is desired adjacent the top and bottom ends of the ear. The use of the sharper curvature needed for the boss at the top and bottom ends of the ear would cause greater than desired amounts of stress in the point under heavy loading. The bosses holding the pin in the opening are therefore offset from the top and bottom ends of the ear so that the point is provided with the broad arcuate transition structures as well as the desired bosses.
In another aspect of the invention, a sandwich pin includes an arm which projects rearward to extend between the lugs and the adapter nose when the pin is assembled in an external locking tooth. The arm stabilizes the orientation of the pin to prevent unwanted turning of the pin in the pin opening. The arm also prevents an erroneous insertion of the pin during assembly of the tooth.
In another aspect of the invention, the point defines an opening adapted to receive a lock pin therein. The point further includes a plurality of recesses along the opening to receive locking detents of the inserted pin. This multiple, independent locking construction between the pin and the point creates a positive locking assembly which alleviates unintended release or loss of the pin from the pin opening.
According to another aspect of the invention, the lock pin has a single elastomeric member which uniquely cooperates with a rigid casing to define a pair of independently depressible protrusions. The elastomeric member includes a front protrusion which engages a face of the adapter nose and a rear protrusion which is inserted into a gap defined between a pair of walls or lugs of the point. The front protrusion tightens the connection of the point onto the adapter nose and the rear protrusion locks the pin to the point. The independently depressible nature of the rear protrusion provides a secure locking function to alleviate unintended release of the pin, isolates the rear protrusion from the front protrusion to lessen the affects on the pin of heavy loading, and enhances the mating receipts of the pin's rigid casing in the pin opening of the point to securely lock the pin to the point even when assembled on a worn and loose fitting adapter nose.